1. Field of the Invention
This invention relates generally to variable speed friction drive transmissions. More paricularly, it concerns such transmissions that have high torque carrying capacities and are capable of providing infinitely variable speed reduction over a substantiailly wide range.
2. Description of the Prior Art
The prior art is replete with disclosures of many different forms of variable speed transmissions. One important class of such transmissions are those which permit infinite variation of the speed of a rotary output shaft being driven by a rotary input shaft. The present invention concerns this class of transmissions.
There are a variety of types of transmissions within the above indicated class, e.g., mechanical torque converters and hydraulic torque converters. The present invention relates to mechanical type torque converters comprising driving balls arranged in constant rolling frictional contact with pairs of inner outer concentric and axially moveable ball races. Such transmissions are generally referred to as variable speed friction drive (VSFD) transmissions. The essential requirements for economical VSFD transmissions for a wide speed range are outlined in my prior U.S. Pat. No. 3,248,96, the disclosure of which is incorporated herein by reference.
I have previously developed a variety of VSFD transmission mechanisms on which I have obtained a number of other U.S. patents including the following:
______________________________________ 2,586,725 3,238,816 3,229,538 3,707,888 3,237,468 3,745,844. ______________________________________
The present invention is basically an improvement in the form of variable speed transmission disclosed in my previous U.S. Pat. No. 3,707,888.
Examples of additional patents related to VSFD transmission mechanisms include:
______________________________________ U.S. Pat. No. 2,701,970 3,793,907 3,258,981 4,480,491 4,503,275 Canadian 526,665 614,725 W. German 2,331,199 3,215,923 Great Britain 1,376,057. ______________________________________
In spite of the extensive development work that has been done on VSFD transmissions as disclosed in the foregoing and numerous other prior patents and publications, there exists a need for further improvements in such type mechanisms. For example, improvements are needed to permit the VSFD transmissions to be made more compact and energy efficient.
Another problem with prior known devices of this class has been that paired ramp portions my get out of phase with when the transmissions are under a no-load condition. Such phase disruptions can seriously damage the mechanism.
A further problem in prior VSFD transmissions of great importance has been the variation in force required to turn the input shaft as the output shaft has been adjusted from low speed to high speed. The present invention offers improvements in VSFD transmissions to correct these deficiencies of the prior known devices.